Wide angle lens

ABSTRACT

A WIDE ANGLE OBJECTIVE LENS HAVING AT LEAST FIVE LENS MEMBERS SEPARATED BY AIR SPACES, OF WHICH TWO CONVERGING LENS MEMBERS, SEPARATED BY A DIAPHRAGM SPACE, ARE FOLLOWED ON THE OBJECT SIDE BY AT LEAST TWO DIVERGING LENS MEMBERS, AND ON THE IMAGE SIDE BY AT LEAST ONE DIVERGING LENS MEMBER, IN WHICH THE AXIAL AIR SPACE BETWEEN THE CONVERGING LENS MEMBER ON THE OBJECT SIDE AND THE PRECEDED DIVERGING MENISCUS LIES BETWEEN 0.002 F AND 0.050 F, AND IN WHICH THE NUMERICAL VALUE OF THE PRODUCT OF THE RATIO OF THE DIFFERENCE BETWEEN THE RADII OF CURVATURE OF THE BOUNDING SURFACES OF THE SAID AIR SPACE TO THE LENGTH OF THE AIR SPACE, AND THE RATIO OF THE RADIUS OF CURVATURE OF THE INNER OF SAID BOUNDING SURFACES TO THE RADIUS OF CURVATURE OF THE CONVEX SURFACE OF THE PAIR OF SURFACES CONCAVE TOWARDS THE DIAPHRAGM IN THE CONVERGING LENS MEMBER ON THE IMAGE SIDE, LIES BETWEEN 1.60 AND 3.9.

350-464 SR T \MMDT OR 395670310 X March 2, 1971 5L5: 3,567,310 WIDEANGLE LENS Filed July 31, 1967 2 sheets-sheet 1 FIG. 1.

,av mum W964 mew 6w March 2, 1971 1.. BERTELE 3,567,810

WIDE ANGLE LENS Filed July 31, 1967 2 Sheets-Sheet 8 11 1: 1 11 11 1 1 12 a/a' s s BY ,ddwvh/ m 122W mm United States Patent US. Cl. 350-176 9Claims ABSTRACT OF THE DISCLOSURE A wide angle objective lens having atleast five lens members separated by air spaces, of which two converginglens members, separated by a diaphragm space, are followed on the objectside by at least two diverging lens members, and on the image side by atleast one diverging lens member, in which the axial air space betweenthe converging lens member on the object side and the preceded divergingmeniscus lies between 0.002 F and 0.050 F, and in which the numericalvalue of the product of the ratio of the difference between the radii ofcurvature of the bounding surfaces of the said air space to the lengthof the air space, and the ratio of the radius of curvature of the innerof said bounding surfaces to the radius of curvature of the convexsurface of the pair of surfaces concave towards the diaphragm in theconverging lens member on the image side, lies between 1.60 and 3.9.

This invention relates to a wide angle objective lens having at leastfive lens members separated by air spaces.

In British patent specification No. 719,162 there are described lenseshaving angular fields of 90 and 100 and an aperture ratio of f 4.5; suchlenses have been known under the name of Biogon. Efforts to increase theaperture still further resulted in an increase of the zonal aberrationto an intolerable extent, unless the length of the lens was increasedvery considerably which was undesirable.

The present invention seeks to provide a desirably short lens having theaforesaid wide angular field, and an aperture ratio of f 2.8 or morewith tolerable zonal aberration.

The invention also seeks to provide lenses of apertures smaller than f2.8 having less zonal aberration than do similar known lenses of thesame aperture.

FIG. 1 is a diagrammatic view of a lens according to one embodiment ofthe invention; and

FIG. 2 is a similar view of a modified embodiment.

The present invention provides a wide angle lens of total focal lengthF, divided into object-side and imageside groups of elements by adiaphragm, wherein each group has a converging member having, adjacentthe diaphragm, an inner negative lens element L L with a concave surfaceremote from the diaphragm and cemented to an adjacent inner convexsurface of a positive lens element L L having a higher refractive indexthan the negative lens element L the outer convex surface of thepositive lens element of the converging member of the image-side grouphaving a radius of curvature r, and a centre of curvature lying on theimage side of the outer convex surface of the positive lens element L ofthe object-side group converging member, the converging member of theimage-side group including a diverging element L having a surfaceconcave towards the diaphragm and spaced from or cemented to the outerconvex surface of the positive lens element L the imageside grouphaving, between the converging member and the image, at least onediverging member L spaced from the converging member; the object-sidegroup having, between the converging member and the object, at least twodiverging members L and L separated from each other by a distance s andfrom the converging member by an 'air space, the diverging member L nextto the converging member being a meniscus concave towards the diaphragmwith a radius r and spaced at distance S, from the adjacent outersurface, of radius r of the positive lens element L the distance s beingbetween 0.002 F and 0.050 F; the lengths of the said radii r r r anddistance s being such as to satisfy the relationship I have found that,if the meniscus diverging member next to the converging member of theobject-side group is brought so close to the coverging member that itsdistance from the latter is within the above stated limits 0.050 F to0.002 F, and if at the same time the mutually facing lens surfaces arecurved more sharply than has hitherto been the case, then a large angleof refraction is obtained. This measure, in conjunction with the pair ofsurfaces, which are concave towards the diaphragm, in the convergingmember of the image-side group, has such favourable influence on theshape of the spherical aberration curve that an aperture ratio of f 2.8or even more can be achieved. The sharp curvature of the mutually facinglens surfaces is achieved when the aforesaid relationship is satisfied,while the aforesaid spacing limits ensure a satisfactory optical path inthe extended equatorial section.

The partial focal length after the converging lens member on the imageside, that is to say without the diverging meniscus on the image side,having regard to the large aperture ratio, should preferably amount tofrom 0.65 to 0.85 times the total focal length F.

The cemented surface (r6), which is concave in the direction of thediaphragm, in the converging member on the object side in the examplesof British Pat. No. 719,162 is thus superfluous since its function istaken over by the air space having the bounding surfaces of radii r andr The following examples of embodiment will be described with referenceto the drawing. The radii, thicknesses, air spaces, and individual lenselement show the index in Roman figures in the group on the object sideand with Arabic numerals in the group on the image side, in both casesincreasing from the diaphragm. Linear dimensions are in millimetres. B1indicates the diaphragm and s is the diaphragm space. If an adjustablediaphragm aperture and a shutter diaphragm are dispensed with, thediaphragm space may become zero. In this case the two converging membersmay be combined to form a single member with a diaphragm incision. InExamples 1 to 4 the radii r;, and r;,' are equal and the surfaces arecemented together, while in Example 5 the two surfaces r and r are notcemented and are separated by a small air space s lnr-nv m P811181 focallength SI -rs after L F The pair of surfaces r /r which are concavetowards the diaphragm and are situated in the converging lens member onthe image side, may be cemented or be left uncemented with a small airspace between them.

It is within the scope of the invention for the outer meniscus Ldisposed on the object side to be in the form of a cemented element orto be split up into two individual lens elements. The same applies alsoto the outer meniscus L disposed on the image side. For the purpose offurther improvements of the correction, cemented surfaces mayadditionally be inserted in other lens elements.

The following numerical table now shows the optical data of five lenseshaving an aperture of f 2.8, with an angular field of about 90 and afocal length of F=l mm. Lenses according to Examples 1 to 4 areillustrated in the accompanying FIG. 1, while a lens according toExample 5 is illustrated in the accompanying FIG. 2.

EXAMPLE 1 tlv=l7.0 1.49388 66.1 fv1==+47.95

tm=36.28 1. 72340 38.0 r1v=+39.72

tn=16.9 1. 67790 55. 5 m=45.35

t1=6.8 1. 57501 41. 3 fr=792.8

tz=29.2 1. 62041 60. 3 ra=29.79

EXAMPLE 2 trv=17.0 1.49388 56. 1 rv1=+47.59

m=37.4 1. 78179 Trv=+38.70

t1r=10.9 1. 67790 55.5 7n=44.22

ti=7.05 1. 58913 61.2 1'g=+35.94

tg=30.05 1.59580 55. 6 Ia=28.73

EXAMPLE 3 Ila v rvu=+280.0 L1 5lV=14-0 1. 48740 70. 0

m=38.55 rv=+69.0 In tm=35.15 1. 83500 37. 2

rrv=+36.02

sr=0.38 m1=+36.908 L3 tn=m. 00 1. 67790 55. 5

m=42.70 L4. ti=5.90 1. 58775 42. 0

a=6.24 n=+797.4 L5 t1 =6.7 1. 56384 50. 8

Tz=+30. 0 Lu t:=28.4 1. 65100 55. 5

n=-28.97 L t|=17.0 1. 72000 43. 8

a1=31.0 =41.75 Lg =93 1. 51009 63. 4

n= -149.34 .Yo'=3l.1

EXAMPLE 4 na r rvn=+287.40 L1 hv=14.90 1. 48749 70. 0

sn=41.04 rv=+73.46 L2" i2m=37.42 1. 83500 37. 2

si=0.40 rm=+39.35 L: tn=21.35 1. 69100 54. 7

m=45.40 L4. tr=6.28 1. 50150 40. 4

a=6.64 r =+1,02l.90 L5 ti=7.13 1. 58913 61. 3

n=+38.31 14..-. tz=26.01 1. 67790 55. 2

r =26.72 L1... t|=22.35 1. 72000 43. 8

EXAMPLE 5 rvn=+267.00 L trv=17.00 1. 40388 66. 1

m=40.80 fv=+07.04 Lg...- tm=35-10 1. 60008 39. 2 rrv=+40.75

t1 =1fi.90 1. 07790 55. 5 rn=48.00

tr=6.80 1. 56138 45. 3 r =-715.00

a=5.76 T =+893.84 L; t.=9.s5 1. 47069 61. a

fz=+34.85 Ll... t2=27-00 1. 55753 67. 3

l0=0.70 r|'=36.87 L1 ta=24.10 1 85000 29. 0

|1==32.00 f5=42.55 In i|=12.50 1. 51823 59. 0

What is claimed is: 1. A wide angle lens of total focal length F,comprising a diaphragm and at least five lens members, the diaphragm andthe lens members being co-axially mounted so as to form object-side andimage-side groups of lens members disposed on respective sides of thediaphragm; each group having a converging member comprising an innernegative lens element mounted adjacent the diaphragm and having aconcave surface remote from the diaphragm, and a positive lens elementhaving an inner and an outer convex surface and a higher refractiveindex than the negative lens element, the said concave surface of thenegative lens element being cemented to the adjacent inner convexsurface of the positive element, the outer convex surface of thepositive lens element of the converging member of the image-side grouphaving a radius of curvature r and a centre of curvature lying on theimage side of the outer convex surface of the positive lens element ofthe object-side group converging member, the converging member of theimage-side group also including a diverging element having a surfaceconcave towards the diaphragm and adjacent the outer convex surface ofthe positive lens element; the image-side group additionally having atleast one divergent member mounted on theimage-side of the convergingmember and spaced therefrom; the object-side group additionally havingat least two diverging members mounted on the object side of theconverging member and spaced therefrom and from each other, thediverging member next to the converging member being a meniscus concavetowards the diaphragm with a radius r and spaced a distance r; from theadjacent outer surface, of radius r of the positive lens element, thedistance s being between 0.002 F and 0.050 F; the lengths of the saidradii r r and r;;, and distance s being such as to satisfy therelationship 2. A lens as claimed in claim 1 in which the concavesurface of the diverging element included in the converging member ofthe image-side group is cemented to the outer convex surface of thepositive lens element.

3. A lens as claimed in claim 1 wherein the converging members areseparated by a space containing the diaphragm.

4. A lens as claimed in claim 1 wherein the partial focal length afterthe converging lens member of the image-side group is from 0.65 F to0.85 F.

5. A wide angle lens according to claim 1 in which the values of r;;, rr and s; are as set forth in the following table:

6. A wide angle lens according to claim 1 in which the values of r r rand s; are as set forth in the following table:

as v

rvn=+274.4 L1 t v=17.0 1. 49388 66.1

rvr=+47.69

m=30.3 rv=+88.03 L; tm=37.4 1.78179 37.1

r v=+a8.70

0r=l.36 f11 =+4l.13 L. t1|=10.9 1.67790 55.5

rn=-44.22 L. t|=6.B 1.58050 40.8

n=946.6 a=6.24 n=+1,190.0 L t|=7.05 1. 58913 61.2

I'Q=+35.94 L| t,=30.05 1.69680 55.6

=23.73 L1 t;=2l.32 1. 80802 40.1

61=34.0 n=41.90 L. n=14.2 1.51112 50.5

7. A wide angle lens according to claim 1 in which the values of r r rand s; are as set forth in the following table:

rv11=+280.0 L1 tiv=14.0 1. 48749 70.0

8n=38-55 rv=+00.0 L: tn1=35J5 1. 83500 37. 2

ar=0.38 m =+36.908 L1 tn=20.00 1. 67790 55.5

rn=42.70 L4 t1=5.90 1.58775 42.0

a=6.24 n=+797.4 L. t1=6.7 1. 50384 60.8

rz=+36.0 L. t,=28.4 1.65160 58.5

fp -28.97 L t;=l7.6 1. 72000 43.8

81=37.0 r -41.75 L8 h=9.3 1 51009 63.4

8. A wide angle lens according to claim '1 m WhlChthe values of r;,, r rand s; are as set forth in the following table:

rvn=+287.40 Lt t1v=14.00 1. 48749 70.0

m=41.04 rv=+73.46 L1, lim=37.42 1. 83500 37. 2

n=0.40 r n=-|-39.35 Ll l5n=2L35 1.00100 54.7

m=45.46 L. tr=0.28 1.50150 40.4

a=0.04 f =+l,021.90 L; t1=7.1a 1. 58913 61.3

f:=+38-31 L|...-.. tz=26.61 1.07700 55.2

8 =39.39 T5=-44A5 L; t.=9.00 1.51112 60.4

7 9. A wide angle lens according to claim 1 in which the values of r r rand s; are as set forth in the following table:

nu I

rvu=+267.00 L t1v=17.00 1 49388 66. 1

m=40.80 rv=+67.64 In t11x=35.l6 1. 66998 39. 2

L1 lia -16.90 1. 67790 56. 5

m=-48.00 L4 t|=6.80 1. 66138 45. 3

a=5.76 r ==+893.84 L; =9. 1. 47069 67. 3

n=+34.86 Ll tz=27.00 1. 55753 67. 3

so=0.70 n'=36.87 L1 h=24.10 1. 85000 29.

a1=32.00 r =-42.55 In l2 =12.50 1. 51823 59. 0

n=l99.70 8n'32.71

References Cited UNITED STATES PATENTS

